Advances in digital compression and availability of international standards and digital networks have created a growing interest in multimedia conferencing systems. There is a trend for many multimedia conferences to be multipoint, i.e., involving three or more participants.
Presently, multipoint videoconferencing is implemented using a centralized multipoint control unit (MCU) which is responsible for providing, among other functions, audio mixing and video switching functions. In the future, MCUs will also provide video mixing to allow participants to view more than one person at a time.
A significant drawback of existing MCUs is a lack of an advantageous networking system. Networking can substantially reduce communication costs: for example, if a large organization has a single MCU located in Atlanta, and two or more conferencing sites are utilized in the West Coast, each West Coast site needs to establish an individual connection to Atlanta, thus incurring high transmission costs. If two MCUs were used, one in the West Coast and the other in the East, only a single coast-to-coast transmission line would be required.
Existing MCUs provide a limited networking capability through cascading. In a cascade, each MCU provides audio mixing independently by decoding the audio bitstreams, mixing, and then re-encoding for transmission. This causes tandem encodings, thus creating long delays and degrading audio quality. The videoconferencing operation degrades upon the addition of video mixing.
Thus, there is a need for a more efficient multipoint multimedia conferencing system that reduces delays while concommitantly improving quality of transmission.